PR #170 for issue #168 - missing raster JPEG

Closes #168

Author: justb4

workshop/jupyter/content/notebooks/05-raster-data.ipynb

@@ -28,8 +28,8 @@
     "\n",
     "A raster captures a continuous phenomenon into a ***regular tessellation*** of space. Within each tile or cell of the raster the value of the phenomenon or variable of concern is constant. The location and size of each cell is perfectly known since the tessellation is regular. This process of collecting a continuous variable into a raster is sometimes referred to as ***discretisation***.\n",
     "\n",
-    "![Raster](https://camo.githubusercontent.com/bf207b7f1a4bc70ae8cf652921320c6ff3a0e280/687474703a2f2f6c65732d656a6b2e637a2f736b6f6c656e692f67726173732f75766f642f5f696d616765732f7261737465722d64657461696c2d64657461696c2e706e67)\n",
-    "*A matrix of values composing a raster*\n",
+    "![Raster](images/raster-matrix.jpg)\n",
+    "*A matrix of values composing a raster from [StackOverflow](http://stackoverflow.com/questions/26705092/plot-a-matrix-values-as-colors)*\n",
     "\n",
     "As many satellites carry various sensors on board, often raster files represent more than one phenomenon or variable. In essence, it is composed by more than one overlapping matrices. These individual matrices are known as ***bands***.\n",
     "\n",